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Subject: Global-Scale Distributed Storage Systems

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  • From: melc AT fashionvictims.com
  • To: Global-Scale Distributed Storage Systems <bluesky AT franklin.metalab.unc.edu>
  • Subject: Re: Grapevine Technical Overview
  • Date: Mon, 27 May 2002 20:11:48 +0200 (CEST)


On Fri, 10 May 2002, Stephen Blackheath wrote:

> In order for someone running a node to know what the contents of a
> file stored on their system is, they have to guess the filename of the
> file it belongs to, and then look up the file map and see if that CHK
> is in the file map. Even if they know the entire contents of the file
> they suspect, this is not sufficient information, due to the CBC mode
> initialization vector. Hence plausible deniability.

Hi,

I've been thinking about the design of anonymous/censorship-resistant file
storage systems (like grapevine) and it seems to me that there is a
problem with this kind of plausible deniability.

Given a file name or identifier it is possible to find out what blocks the
file consists of (it must be, otherwise you can't download all the blocks
of the file). Also each block is (I assume) uniquely identified by its
CHK. Thus, given the name (or some other identifier) of a forbidden file,
it is possible to create a list of CHKs that make up that file. Given that
such a list can be made, the "thought police bureau of censorship" simply
have to actively discover forbidden files (e.g. using a grapevine search
engine), determine the CHKs of the blocks that make up those files,
compile and regularly publish a list of forbidden block CHKs and make it
illegal to request, host or relay any such blocks. Once they've done that
it is simply a question of finding out (e.g., by making grapevine requests
for forbidden blocks, or through more physical "break down the door"
techniques) who is requesting, hosting or relaying these blocks and cart
them off to jail.

Is there a way to foil this kind of attack?

Ihor.










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